The present invention relates in general to blast-furnace tap-hole plugging mix compositions and has specific reference to an improved plugging mix of this character.
It is known notably through Werking U.S. Pat. No. 2,709,659 to use a product comprising about 80% of clay and ground brick, and a binder consisting:
-EITHER OF 10 TO 12% OF COAL TAR AND 5 TO 7% OF AN ALDEHYDE SUCH AS FURFURALDEHYDE,
-OR 15 TO 25% OF PHENOL RESIN WITH AN ACID OR BASIC CATALYST ADDITIVE.
Unfortunately, this mix sets very rapidly in the plugging machine cylinder, thus requiring the dismantling thereof after each cast. This causes a considerable loss of time. On the other hand, in the first case the tar is burned and the noxious vapours thus released surround the tap-hole and mud-gun. Besides, the considerable proportion of light organic substances leads in actual practice to serious inconveniences such as projections, flames, etc.
It is also known through the papers published by Dr. Walter HORN in "Stahl und Eisen", Volume 23, pages 1497 to 1502 to prepare an anhydrous tap-hole plugging mix comprising 70% of silicious clay, 10% coal or coke, and 20% tar. However, the coking process is relatively slow, large amounts of tar vapours are released and the uncured tar produces dangerous cast-iron projections.
To avoid these inconveniences it is know through Elby U.S. Pat. No. 3,607,809 to employ a tap-hole plugging mix comprising 70% of a mixture of sand and clay in such proportions that the percentage of alumina is 1 or 2% above the eutectic value, 10% of ground coal or coke, a binder consisting of only 15 to 17% of liquid tar plus 3 to 4% of a liquid resin thermostable up to 200.degree. F. (392.degree. F.) derived from the amino or phenoplast group, and 1 to 3% of a setting retarding agent. With this composition a rapid coking or carbonization, of the order of 10 to 15 minutes, a very low release of noxious tar vapour, a negligible deposit in the plugging machine cylinder and no cast-iron projections whatsoever were observed.
The explanation of the phenomenon having led to such advantageous results is that certain amino or phenoplast substances constitute a kind of carbonaceous skeleton in which all the tar is burned off.
However, a certain degree of release of coal tar fumes is still observed during the plugging operation due to the excess mix falling into the hot trough, these fumes creating discomfort to the founders during the cleaning of this trough.
Now, it was found, according to the present invention, that a tap-hole plugging mix composition could be developed which provides results at least as satisfactory as those obtained with the above-defined anhydrous mixes while eliminating or significantly reducing any release of noxious fumes.